I guess it is a relevant point, if you currently can't get erections (or possibly aren't bothered) then prospects are better not trying to spare nerves. There ought to be a similar discussion about fertility, since prostatectomy involves a form of vasectomy, the only way you would be able to father children is through frozen sperm.
But it highlights the way the surgeon's plans carry a certain risk, the precise situation and ease of operation aren't known in advance. In my case the decision was made to spare the nerves on one side - but when the pathology came back it turned out there was a small positive margin on that side and some cells of a higher grade than had been picked up on the biopsy. I have recently, six years later, needed salvage radiotherapy.